Bunch-excited wakefield in dielectric waveguide with hollow plasma channel

Abstract

Wakefield excitation by a single relativistic electron bunch in a plasma–dielectric accelerating structure has been studied both analytically and numerically. The structure represents a dielectric-loaded cylindrical metal waveguide, which has partially plasma-filled channel (the hollow plasma channel) to transport charged particles. Assuming the linear regime of excitation, analytical expressions have been derived for the longitudinal and radial wakefields generated by a finite-size electron bunch. Axial profiles of wakefield component amplitudes have been studied, and their mode and spectrum analyses have been performed. Numerical calculations, based on the constructed theory, are presented for dielectric (quartz) waveguide with inner and outer radii of 500μm and 600μm, and hollow plasma channel with plasma density of 2.0⋅1014cm−3 and inner plasma radius of 200μm. Drive bunch is an annular 5 GeV, 3 nC electron bunch with length of 250μm, and radius of 450μm, moving along the waveguide axis without transverse offset. An analysis of a dispersion of the dielectric waveguide with hollow plasma channel demonstrated the presence of two surface eigenwaves, which are absent in corresponding dielectric-loaded waveguide without plasma filling. Numerical studies showed the possibility of acceleration of both electron and positron test bunches with their simultaneous radial focusing. Fourier analysis of a transverse wakefield demonstrated that a main contribution to its amplitude belongs to a backward plasma surface eigenwave. Furthermore, the electron bunch-driven wakefield excitation has been PIC-simulated numerically for the quasi-linear regime. The comparative analysis of the data resulting from analytical studies and the ones obtained by numerical simulation has demonstrated qualitative agreement between the results.